vin ECHINODEBMATA— MORPHOLOGY OF SKELETON 343 



Fig. 303. — Toxopneustes droebachiensis juv., 4 mm. in diam. The whole system of plates 

 spread out in one plane (after Lov6n). B, Peristome plates. D, teeth. 



marked by common characters, and are distinguished from the plates K, IIS, Ilia, 

 IV6, Va, which also resemble one another. These different characters are, it is true, 

 often not very evident. 



